The present invention relates to a vibration damping apparatus using a magnetic circuit, and more particularly to a vibration damping apparatus using a magnetic circuit which can be used as a component in the suspension unit of a vehicle seat, an electric train seat, or a boat seat, an engine mount, or the like.
A variety of damping materials, dampers, and control techniques have been commonly used to reduce vibration and noise caused by a machine or an apparatus which itself is typically constructed of a low damping material in order to ensure its rigidity.
Damage to human body and its nervous system due to their exposures to vibration has become a serious problem with the ever increasing vehicle speed. Such damage shows many symptoms such as fatigue, headache, stiffness of shoulders, lumbago, and amblyopia. In general, vibration isolation is achieved by a damping apparatus with properly matched springs such as metal springs or air springs and damping materials such as rubber, viscoelastic materials, or dampers. However, the dynamic magnification of the damping apparatus tends to correlate to its loss factor. More particularly, a reduction in dynamic magnification to improve a low-frequency characteristic of the damping apparatus tends to reduce the loss factor, resulting in the damping apparatus being too firm and a poor damping efficiency at high-efficiency. An increase in the loss factor of the damping apparatus to improve a high-frequency characteristic leads to an increase in is dynamic magnification, resulting in the damping apparatus being too soft and a poor damping efficiency at low-frequency. Many attempts have been made in the prior art to suppress vibration by semi-active control or active control, or by using a passive damper containing a dynamic vibration damper.
A damping apparatus containing a magnetic spring device has been recently disclosed. Also, a vibration damping apparatus having a spring constant being substantially near zero by incorporating a damping member such as a metal spring and a cushioning member such a rubber material is disclosed. However, the disclosed vibration damping apparatus tends to have a high manufacturing cost and require a complicated manufacturing process. Thus, it is highly desirable to develop a novel damping apparatus which is easier to manufacture and has a spring constant being substantially near zero within a predetermined range of displacement. Such an apparatus would simplify the structure and the maintenance and reduce the size of a suspension unit, an engine mount, or the like.
The present invention is made to overcome the aforesaid disadvantage of the prior art, and its object is to provide a vibration damping apparatus using a magnetic circuit which is easier and less expensive to manufacture.
The present inventor has made investigation to solve the aforesaid problem, and found out that if a negative spring constant (elastic constant) is created by using an attracting magnetic circuit, a total spring constant (elastic constant) within a predetermined range of displacement can be set to substantially near zero by a very simple configuration by adding an elastic member having a positive spring constant (elastic constant) with the same value as the negative spring constant, leading to the accomplishment of the present invention.
To attain the aforesaid object, in accordance with one aspect of the present invention, a vibration damping apparatus using a magnetic circuit is provided. The vibration damping apparatus using the magnetic circuit comprises: a moving member placed to move relatively away from and close to a magnet and made of a magnetic material which generates an attraction force between the moving member and the magnet; an elastic member urging the moving member in a direction in which the moving member approaches the magnet; and a cushioning member mounted on a predetermined position to prevent the moving member from coming in contact with the magnet, wherein a total spring constant obtained by a combination of the attraction force between the magnet and the moving member with, an elastic force of the elastic member is set to substantially zero within a predetermined range of displacement.
In a preferred embodiment of the present invention, the elastic member comprises a metal spring.
In a preferred embodiment of the present invention, the cushioning member comprises a rubber.
In accordance with another aspect of the present invention, a vibration damping apparatus using a magnetic circuit is provided. The vibration damping apparatus using the magnetic circuit comprises: a moving member placed to move relatively away from and close to a magnet and made of a magnetic material which generates an attraction force between the moving member and the magnet; an elastic member urging the moving member in a direction in which the moving member approaches the magnet; a cushioning member mounted on a predetermined position to prevent the moving member from coming in contact with the magnet; and an operating member connected to the moving member and placed so that the magnet is positioned around the operating member, moving in a direction in which it traverses a magnetic flux generated in a space in the magnet with the approaching and leaving movement of the moving member, and made of a conductive material which generates a damping force by an electromagnetic inductive action, wherein a total spring constant obtained by a combination of the attraction force between the magnet and the moving member with an elastic force of the elastic member is set to substantially zero within a predetermined range of displacement.
In a preferred embodiment of the present invention, the elastic member comprises a metal spring.
In a preferred embodiment of the present invention, the cushioning member comprises a rubber.